Stain on frame

Do you use one of those bike stands with the jaw that holds the top tube?
This marking is suggestive of a pressure point from this type of jaw. Hence, the length of the marking.

Ha! (only 2 weeks later).

I Googled around and eventually discovered a post on some bike forum where some chap was asking about the marks left on his and his wifes white frames after the bikes had been transported on a car rack thingy with rubber protective pads.
I do indeed use a bike stand with the jaw that holds the top tube. The jaw/clamp is some sort of rubber compound and the Jackson has been held in it.
So the next thing is how to remove the stain.

Thanks